This invention relates to polyphenylene ethers, and more particularly to functionalized polyphenylene ethers useful for the compatibilization of copolymer blends.
Polyphenylene ethers are a widely used class of thermoplastic engineering resins characterized by excellent properties including hydrolytic stability, dimensional stability, toughness, heat resistance and dielectric properties. It is of continuing interest to introduce these desirable properties into polymer blends by incorporating the polyphenylene ethers as blend constituents. This is often difficult, however, since the polyphenylene ethers are incompatible with many other polymers.
A strategy frequently used to compatibilize polyphenylene ethers with other polymers is to introduce into the polyphenylene ether functional groups which are reactive with said other polymers, enabling the formation of copolymer-containing compositions in which the copolymers serve as compatibilizers. For example, polyphenylene ethers containing carboxylic acid functional groups or derivatives thereof can form copolymers with such other polymers as polyamides, hydroxy-terminated polyesters and epoxy group-containing polymers.
Carboxy or carboxy-derived groups (e.g., anhydride groups) have been introduced into polyphenylene ethers by reaction through the hydroxy end groups with such compounds as trimellitic anhydride acid chloride, by grafting reactions with such compounds as maleic anhydride or fumaric acid, and by redistribution with acidic compounds such as p-hydroxyphenylacetic acid. Redistribution reactions are often of particular interest since they may be conducted under relatively mild conditions, typically including temperatures not substantially greater than 100.degree. C. and the presence of non-destructive catalysts such as diaryl peroxides and quinones and relatively inert solvents such as toluene. The redistribution reaction results in a breakup of polymer molecules into lower molecular weight molecules containing the desired carboxylic acid or other functional groups.
Redistribution with the aforementioned acidic compounds is somewhat difficult, however, since said compounds are not adequately soluble in solvents such as toluene. Moreover, the mechanism of the redistribution reaction is such that only low levels of such compounds can be incorporated in the polyphenylene ether, owing in part to substitution in the para position which makes that position unavailable for reaction.
U.S. Pat. No. 5,880,221 discloses attempts at redistribution of polyphenylene ethers with various aryl-substituted alkanoic acids. It was found that whereas carboxy phenols bearing two phenolic hydroxyl groups and alkyl substituents, ortho to the phenolic hydroxy groups, such as 4,4-bis(3,5-dimethyl-4-hydroxyphenyl)pentanoic acid, did incorporate, simple phenols such as p-hydroxyphenyloctanoic acid did not. Interest continues, therefore, in the development of improved functionalization strategies employing other carboxylic acids, especially those of simpler molecular structure than the aforementioned bisphenolic acid.
Japanese Kokai 5/59,270 and 5/59,272 disclose reaction products of epoxy- and carboxy-functionalized olefin polymers with copolyphenylene ethers in which a portion of the structural units contain a --(CH.sub.2).sub.3 OH group. Said copolyphenylene ethers are produced by copolymerization via oxidative coupling of two phenols, one containing and one not containing said group. There is no disclosure of a copolyphenylene ether containing a carboxyalkyl group.